Automatic choke for carburetor



March 2, 1965 F. w. HAMILTON 3,171,868

AUTOMATIC CHOKE FOR CARBURETOR Filed Aug. 1, 1961 INVENTOR. flawed: M/717rr27f071.

BY #WQLIE/W United States Patent 3,171,868 AUTOMATIC CHOKE FOR CARBURETGR Francis W. Hamilton, Southfield, Mich, assignor to Chrysler Corporation, Highland Park, Mich, a corporation of Delaware Filed Aug. 1, 1961, Ser. No. 128,407 Claims. (Cl. 261-39) This invention relates to fuel charging systems for internal combustion engines and in particular to an improved carburetor for an automobile engine which prevents engine stalling due to lean fuel-air mixture at idle following a cold start, without providing an overrich mixture at road load.

It is customary to provide a thermostatically controlled choke valve to restrict the fuel-air induction conduit of a carburetor during cold starting conditions. Immediately after the cold engine is started, the extent of choking required for engine idling is appreciable, but decreases rapidly in the first few seconds of idling in consequence of engine heating and frictional heating of the bearing parts which rapidly reduce the frictional load on the engine.

In order to prevent the engine from stalling immediately after a cold start, the bi-metallic thermostat spring controlling the position of the choke valve is usually predetermined to allow opening of the choke valve approximately of are from the closed position. Within a few seconds after the engine is started, the aforesaid heating effects, particularly in the bearing parts, enable the engine to idle with a choke opening of approximately of arc. However, the thermostat choke control spring is not readily responsive to these heating effects and restricts the choke opening to the 20 of are for the first several minutes of idling. During this time, the fuel-air mixture will be excessively rich and poor fuel economy will result.

The initial opening of the choke valve to the idling position in opposition to the force of the themostatic choke control spring is commonly accomplished by pressure actuated means operatively connected with the choke valve and responsive to the low pressure in the induction conduit downstream of the usual throttle valve. When the throttle valve is opened beyond the idling position for operation of the engine at road load conditions, the thermostatic spring normally required to prevent engine stalling within the first few seconds after a cold start exerts too strong a closing force on the choke valve for road load conditions, with consequent poor fuel economy.

An object of the present invention is therefore to provide a simple, economically manufactured and highly eflicient choke control for the carburetor of an automobile engine which enables the use of a comparatively lightweight thermostatic spring that readily yields to enable the opening of the choke valve during operation of the cold engine under road load conditions, yet which affords optimum choking to enable rapid starting of the engine without stalling or die-out during cold conditions.

Another object is to provide such a choke control .wherein the pressure actuated means operates in stages to open the choke valve to a cold idling position to prevent engine stalling or die-out immediately after a cold start when the low pressure applied to the pressure actuated means is within a first range, and to open the choke valve to a road load condition when the low pressure applied to the pressure actuated means is within a second pressure range lower than the first pressure range, thereby to assure economical operation of the engine while being driven in a cold condition. The pressure actuated means is in communication with the induction conduit by means of ports located both upstream and downstream of the throttle valve when the latter is in is cold idle position, thereby to communicate said first pressure range to the 3,171,868 Patented Mar. 2, 1965 pressure actuated means, the upstream port being located downstream of the throttle valve when the latter is opened to a driving position, thereby to communicate the second pressure range to the pressure actuated means.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

FIGURE 1 is a schematic view substantially through the mid-section of a carburetor embodying the present invention.

FIGURE 2 is a fragmentary view taken in the direction of the arrows substantially along the line 22 of FIG- URE 1.

FIGURE 3 is a fragmentary view showing a modification of the communication between the pressure actuated choke control mechanism and the induction conduit at locations upstream and downstream of the throttle valve in the idle position.

It is to be understood that the invention is not limited in its application to the details of construcion and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to FIGURE 1, a particular embodiment of the present invention is illustrated by way of example comprising a carburetor 10 which may be of conventional construction having an upper annular attachment rim 11 for an air cleaner and a central fuel-air induction condnit 12, whereby combustion supporting air enters at the top. A large venturi 13 is formed integrally with the side walls of the induction conduit 12 and a small venturi 14 discharging at the throat of the venturi 13 is suitably supported with the conduit 12. Fuel is admixed at the region of the venturis by means of a nozzle 14a discharging in accordance with customary practice into the small venturi 14. The fuel-air mixture is discharged from the lower end of the conduit 12. Also idle fuel is added via the customary idle jet 10a located downstream of valve The discharge of the fuel-air mixture is controlled by a throttle valve 15 pivotally mounted on a transverse shaft 16 at a location downstream of the venturi 13. A thermostatically controlled choke valve 17 pivotally mounted on transverse shaft 18 is provided in accordance with conventional practice upstream of venturis 13 and 14 for the purpose of providing fuel enrichment during cold operation of the engine.

The shaft 18 extends through the side wall of the conduit 12 and is splined to a crank arm 19 pivotally connected at 20 to a vertically shiftable actuating arm 21 having its lower end pivotally connected at 22 to a crank arm 23 pivotal about the axis of a fixed spindle 24. A bi-metallic thermostat spring element 25 having one end secured to the spindle 24 extends spirally around the latter and terminates in a free end 26 engaging the lower end of arm 21 at the region of pivot 22. In the usual instance, the thermostat element 25 will be located so as to be responsive to engine temperature. During cold conditions, the thermostat element 25 is under tension yieldingly urging shaft 21 upward and crank arm 19 clockwise so as to urge choke valve 17 toward the closed position. As the engine temperature rises, the tension in thermostat spring or element 25 relaxes to enable opening of choke valve 17 to a progressively greater extent under any given condition of airflow in the induction conduit 12.

In order to supplement thermostat spring 25 in conerases trolling the position of choke valve 17 during the initial stages of engine operation after a cold start, a pressure cylinder 27 is provided integrally with the sidewall of carburetor and is in communication with the induction conduit 12 by means of a duct 29. Reciprocal axially within cylinder 27 is acylindrical piston 28 having a closed left end 28a partitioning'cylinder 27 into a low pressure part 30 in communication with duct 29 and a high pressure part 31in communication with conduit 12 via vent opening 32 located upstream of choke valve 17. The left end of cylinder 211s closed by a plate 33 An arm 34 extending through opening 32 is pivotally connected at 35 to piston 28 and at 36 to the swinging of a crank arm 37 splined .to shaft 18.

The outer cylindrical wall of piston 28 is in fluid seal- 7 ing engagement with the inner cylindrical wall of cylin- 'der 27 to prevent appreciable leakage of air around the piston 28 when the latter is at its extreme rightward position whe-r eat choke valve 17 is closed. An axially extending groove 38 is provided in the left side-wall portion of cylinder 27 so as to communicate with an annular groove 39 formed in the outer surface of piston 28 when the latter is shifted leftward from the closed position to a first stage or'coldidling position illustrated. The groove 39 communicates with the interior 31 through a restricted bleed port 40, so asto bleed high pressure from the cylinder part 31' into the cylinder part 30 when the piston 28 is at the first stage position illustrated.

A pair of diametrically opposed axially extending slots 41 are provided in the right end of piston 28 to effect communication between cylinder parts 31 and 30 when piston 28 is shifted leftward from the first stage shown to 'a secon d stage position illustrated in phantom. The upper end of duct 29 communicates with cylinder portion 30 at the region of groove 38. V The lower end of duct 29 communicates with conduit 12 through'a restricted downstream port 42 and an upstream slot or port 43. The port 42 is located downstream of throttle valve 15, whereas port 43 is located immediately upstream of the upper edge of. throttle valve when theilatter is slightly open at a fast or cold idle position illustrated.

In accordance with the foregoing construction, when theengine is first'started in a cold condition, the 'conventional carburetor fast idle mechanism in cooperation with thermostat 25 will maintain throttle valve 15 at'the position i-llustratedduring engine idling. The low pressure in conduit 12 downstream of valve 15 will be communicated'v'ia port 42 and duct 29 to the low pressure side 30 of cylinder 27. This low pressure will be maintained at a value appreciably higher than the pressure downstream of valve 15 by reason of the upstream port 43 which partially bypasses cylinder portion 30 from the low pressure at port '42.

The ports 42 and 43 are dimensioned with respect to the cross-sectional area of piston 28 and the force of thermostat spring 25 so as to cause immediate leftward movement of piston 28 to the first stage position during cause leftward movement of piston 28 to the second stage position illustrated in phantom. At this position, the lower slot 41 will be in communication with groove 38 to prevent further leftward'rnovement of piston 28 until the tension in [thermostat spring 25 is relaxed by warm ing of the engine. In the above regard, port 43 comprises a horizontally-extending slot in the side-wall of conduit 12, FIGURE 2, so that an optimum pressure decrease in duct 29 will result with a minimum of opening of throttle valve 15 from the fast idle position illustrated.

The extent of opening of choke valve 17 at the first and second stage positions of piston 28 will depend upon the operating characteristics of the engine and carburetor 10. In ione'specific type of carburetor construction, a choke valve opening of approximately degrees at the first stage or cold idle position and approximately 40 at the second stage or cold road loadoperating position has been found satisfactory to prevent engine stalling immediately after a cold start, while obtaining improved economy during operation at the cold road load condi tion. a

The present construction eliminates the problem of engine stalling immediately after a cold start, regardless of the temperature condition of thermostat spring 25. According-1y, greater freedom is made possible in the selection of a thermostat spring having the proper characteristics to assure efiicient operation both during and after the warm-upperiod. This is true because it is no longer necessary to make an-arbitary compromise between efficient operation during engine starting and subsequent conditions of operation. V

FIGURE 3 illustrates a modification wherein the overall construction is the same as illustrated in FIGURE 1, the only, difference being that upstream port 43 opens from a valve chamber 44 in communication with port 42 by a bypass duct 45. A spherical check valve 46 nor- 'mally closes duct 45, so that the" low pressure commu- ""The restricted port 42 in FIGURE 3 is dimensioned with respect to restricted por't40 so that when the throttle valve 1 5 is in the idle position shown, the resultant low pressure in cylinder, part will be sufficient to maintain piston 28 at the first stage position shown regardless of the cold temperature condition of thermostat spring 25. As the engine temperature increases andthe tension in spring 25 relaxes sufficiently, piston 28 will then move progressively to the second stage position illustrated in phantom. This latter action will result with the strutture of either FIGURE 1 or FIGURE 3. It is to be noted however in regard to FIGURE 3, inasmuch as check valve 46 prevents a partial bypassingiof cylinder part 30 from the low pressure at port 42, the restriction of the latter in FIGURE 3 will ordinarily be greater than V I the restriction ofport '42 in FIGURE 1.

engine idling, as illustrated, regardless of the temperature'condition of the engine and the choke valve closing force exerted by spring 25. At this position, r estrictecl port will be in communication with groove '38 to prevent further leftward movement of piston 28 during engine idling until the tension in thermostat spring beyond the cold idling or fast idle position illustrated so asfto drive or operate the vehicle 'under'road load condi-' t-ions, port 43 will then' be downstream of the throttle valve 15 and the'lo w pressure communicated. byduct 29 to cylinder 'part 30' will be substantially decreased to FIGURE 1. position until subsequent warming of the engine relaxes the tension in thermostat spring 25. V

When the throttle valve v15 is opened beyond the idle position illustrated, so that port 43 is downstream of the throttle valve, check valve 46 immediately opens to bypass restriction 42 and. communicate the low pressure of conduit 12 downstream of valve 15 immediately to the low pressure portion 30, so as to cause movementof piston 28 to the second stage position illustrated in phantom, Piston 28 will remain at the second stage 1 I claim:

I 1. In a fu'elcharging system for an automotive internal combustion engine, a fuel-air induction conduit,- a choke valve and a throttle valve arranged in said conduit, temperature responsive means for yieldingly urging said choke valve in a closing direction during cold, operation of said engine, pressure'actuated means operable in opposition to said temperature responsive means for shiftin'g saidchoke' valve" to an engine idling position adapted to effect sufiicient fuel enrichment to assure engine idling after a cold start, duct means connecting said pressure actuated means with said conduit at a location downstream of said throttle valve and also at a location upstream of said throttle valve during engine idling, said throttle valve having an edge movable to a position upstream of said upstream location when said throttle valve is opened beyond a fast idle condition.

2. In a fuel charging system for an automotive internal combustion engine, a fuel-air induction conduit, a choke valve and a throttle valve arranged in said conduit, temperature responsive means for yieldingly urging said choke valve in a closing direction during cold operation of said engine, pressure actuated means operable in opposition to said temperature responsive means for shifting said choke valve to an engine idling position adapted to effect sufficient fuel enrichment to assure engine idling after a cold start, duct means connecting said pressure actuated means with said conduit at a location downstream of said throttle valve and also at a location upstream of said throttle valve during engine idling, said throttle valve having an edge movable to a position upstream of said upstream location when said throttle valve is opened beyond a fast idle condition, the communication between said pressure actuated means and conduit comprising a slot extending transverselyin the sidewall of said conduit to effect an optimum change in the area of communication between said conduit and pressure actuated means with a minimum change in the opening of said throttle valve.

3. In a fuel charging system for an automotive internal combustion engine, a fuel-air induction conduit, a choke valve and a throttle valve arranged in said conduit, temperature responsive means for yieldingly urging said choke valve in a closing direction during cold operation of said engine, a pressure actuated member operably connected with said choke valve, a duct having a downstream port in communication with said conduit at a location downstream of said throttle valve and connect ing said port with said member to actuate the latter to urge opening of said choke valve in opposition to sa1d temperature responsive means when said throttle valve is at an idle position, and means partially bypassing the connection between said member and downstream port comprising a bypass duct connected with the first named duct and having an upstream port In communication with said conduit at a location immediately upstream of said throttle valve when the latter is at said idle position, said upstream port being downstream of said throttle valve when the latter is opened slightly beyond said fast position.

4. In a fuel charging system for an automotive internal combustion engine, a fuel-air induction conduit, a choke valve in said conduit, 21 throttle valve in said conduit movable from a closed position to a fast idle position during cold starting of said engine and being openable beyond said fast idle position to a driving position, temperature responsive means for yieldingly urging closing of said choke valve to effect fuel enrichment during cold starting and operation of said engine, staged pressure actuated means operatively connected with said choke valve and responsive to a first range of low pressures for shifting to a first stage in opposition to said temperature responsive means for opening said choke valve to a cold idling position adapted to assure idling of said engine while in a cold condition, said staged pressure actuated means being responsive to a second range of low pressures lower than said first range of low pressures for shifting to a second stage in opposition to said temperature responsive means for opening said choke valve to a cold driving position adapted to asusre econom ical driving of said engine while in the cold condition, and duct means connecting said pressure actuated means With said conduit at locations both upstream and downstream of said throttle valve when the latter is in its idle position, thereby to communicate said first pressure range to said pressure actuated means, said upstream location being immediately upstream of said throttle valve in the fast idle position and being downstream of said throttle valve in said driving position to effect communication of said second pressure range to said pressure actuated means.

5. In a fuel charging system for an automotive internal combustion engine, a fuel-air induction conduit, a choke valve in said conduit, a throttle valve in said conduit movable from a closed position to a fast idle position during cold starting of said engine and being openable beyond said fast idle position to a driving position, temperature responsive means for yieldingly urging closing of said choke valve to effect fuel enrichment during cold starting and operation of said engine, staged pressure actuated means operatively connected with said choke valve and responsive to a first range of low pressures for shifting to a first stage in opposition to said temperature responive means for opening said choke valve to a cold idling position adapted to assure idling of said engine while in a cold condition, said staged pressure actuated means being responsive to a second range of low pressures lower than said first range of low pressures for shifting to a second stage in opposition to said temperature responsive mean for opening said choke valve to a cold driving position adapted to assure economical driving of said engine while in the cold condition, and duct means connecting said pressure actuated means with said conduit at locations both upstream and downstream of said throttle valve when the latter is in its idle position, thereby to communicate said first pressure range to said pressure actuated means, said upstream location being downstream of said throttle valve in said driving position to effect communication of said second pressure range to said pressure actuated means.

6. In the combination according to claim 5, said staged pressure actuated means comprising a pressure chamber, a shiftable pressure actuated member partitioning said chamber into a low pressure part and a high pressure part, said duct means being connected with said low pressure part, said high pressure part being connected with a source of high pressure upstream of said choke valve, restricted bleed means for bleeding said high pressure into said low pressure part when said member is shifted to said first stage, second bleed means for bleeding said high pressure into said low pressure part when said member is shifted to said second stage, said member being operatively connected with said choke valve to actuate the latter.

7. In the combination according to claim 5, said staged pressure actuated means comprising a pressure chamber, a shiftable pressure actuated member partitioning said chamber into a low pressure part and a high pressure part, said duct means being connected with said low pressure part, said high pressure part being connected with a source of high pressure upstream of said choke valve, said member being shiftable in response to the pressure differential between said low and high pressure parts, restricted bleed means for bleeding said high pressure into said low pressure part when said member is shifted to said first stage, second bleed means for bleeding said high pressure into said low pressure part when said member is shifted to said second stage, said restricted and second bleed means being cooperable in parallelism with each other when said member is at said second stage, and said member being operatively connected with said choke valve to actuate the latter.

8. In a fuel charging system for an automotive internal combustion engine, a fuel-air induction conduit, a choke valve and a throttle valve arranged in said conduit, temperature responsive means for yieldingly urging said choke valve in a closing direction during cold operation of said engine, pressure actuated means operable in opposition to said temperature responsive means for shifting said choke valve to an engine idling position adapted to efiect sufiicient fuel enrichment to assure engine idling after a cold start, duct means connecting said pressure actuated means withsaid conduit at a location downstream of said throttle valve, a bypass port opening into said conduit at a location upstream of said throttle valve when said engine is idling, said duct means also connecting said bypass port with said pressure actuated means, a one way check valve normally closing said bypass 'duct from said pressure actuated means when the pressure thereat is less than the pressure at said bypass port, said throttle valve having an edge movable to a position upstream of said upstream location when said throttle valve is opened beyond a fast idle condition.

9. In a fuel charging system for an automotive internal combustion engine, a' fuel-air induction conduit, a choke valve in said conduit, a throttle valve in said conduit movable from a closed position to a fast idle posi tion during cold starting of said engine and being openable beyond said fast idle position to a driving position,-

temperaturej responsive means for yieldingly urging closing of said choke valve to elfect fuel enrichment during cold starting and operation of said engine, staged pressure actuated means operatively connected with said choke valve and responsive to a first range ofilow pressures for shifting to a first stage in opposition to said temperature responsive means for opening said choke valve to a'cold idling position adapted to assure idling of said engine while in a cold condition, said staged pressure actuated means being responslve to a second range of low pressures lower than said first range of low pressures for shifting to a second stage in opposition to said temperature responsive means for opening said choke valve to a'cold driving position adapted to assure economical driving of said engine while in the cold condition, and duct means connecting'said pressure actuated means with said conduit at a location downstream of said throttle valve when the latter is in its idle position, a restriction in said duct means cooperable with said pressure actuated means to efiect communication of said first pressure range thereto andto cause shiftingfof the means is less than the pressure at the last named location,

the last named location being downstream of said throttle valve when the latter is in said driving position to effect communication of said second pressure range to said pressure actuated means.

10. In the combination according to claim 9, said staged pressure actuated means comprising a pressure chamber, a shiftable pressure actuated member operatively connected with said choke valve to actuate the latter and partitioning said chamber into a low pressure part and a high pressure part, said duct means being connected with said low pressure part, said high pressure part being connected with a source of high pressure upstream of said choke valve, restricted bleed means for bleeding said hig'hpressure into said low pressure part when said member is shifted to said first stage "and being cooperable with the restriction to maintain the pressure in said low pressure part within said first pressure range when said throttle valve isat the idle position, second bleed means for bleeding said high pressure into said low pressure part when said member is shifted'to said second stage and effective for maintaining said second pressure rangein 'said low pressurev part when said throttle valve is shifted to said driving position.

' References Cited by the Examiner UNITED STATES PATENTS 2,523,798 9/50 Winkler. 2,538,570 1/51 Kittler.

2,918,266 12/59 Hamilton.

HARRY B. THORNTON, Primary Examiner. EUGENE F. BLANCHARD, Examiner. 

1. IN A FUEL CHARGING SYSTEM FOR AN AUTOMOTIVE INTERNAL COMBUSTION ENGINE, A FUEL-AIR INDUCTION CONDUIT, A CHOKE VALVE AND A THROTTLE VALVE ARRANGED IN SAID CONDUIT, TEMPERATURE RESPONSIVE MEANS FOR YIELDINGLY URGING SAID CHOKE VALVE IN A CLOSING DIRECTION DURING COLD OPERATION OF SAID ENGINE, PRESSURE ACTUATED MEANS OPERABLE IN OPPOSITION TO SAID TEMPERATURE RESPONSIVE MEANS FOR SHIFTING SAID CHOKE VALVE TO AN ENGINE IDLING POSITION ADAPTED TO EFFECT SUFFICIENT FUEL ENRICHMENT TO ASSURE ENGINE IDLING AFTER A COLD START, DUCT MEANS CONNECTING SAID PRESSURE ACTUATED MEANS WITH SAID CONDUIT AT A LOCATION DOWNSTREAM OF SAID THROTTLE VALVE AND ALSO AT A LOCATION UPSTREAM OF SAID THROTTLE VALVE DURING ENGINE IDLING, SAID THROTTLE VALVE HAVING AN EDGE MOVABLE TO A POSITION UPSTREAM OF SAID UPSTREAM LOCATION WHEN SAID THROTTLE VALVE IS OPENED BEYOND A FAST IDLE CONDITION. 